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  4. Adjust Elevations Command
  1. Home
  2. Knowledge Base
  3. GeoHECRAS
  4. Adjust Elevations Command
  1. Home
  2. Knowledge Base
  3. Map View
  4. Adjust Elevations Command
  1. Home
  2. Knowledge Base
  3. Working with a HEC-RAS Project
  4. Adjust Elevations Command

Adjust Elevations Command

The Adjust Elevations command is used to set or adjust elevations for a portion of an existing elevation grid. The user can interactively draw (or select) polygons on the Map View and then define the corresponding elevation value, which can then be merged with the source elevation grid in order to create a revised elevation grid. In addition, this command allows the user to specify the coordinate reference system (CRS) of the final revised elevation grid. The command facilitates creating a more accurate representation of a model’s geometry, for example by setting a lake or reservoir bottom elevation.

Follow the steps below to use the Adjust Elevations command:

  1. From the Terrain ribbon menu, select the Adjust Elevations command.
    Terrain Ribbon Menu - Adjust Elevations Command
  2. The Adjust Elevations dialog box will be displayed.
    Adjust Elevations Dialog Box

The following sections describe the Adjust Elevations command and how to interact with the above dialog box.

Selecting Elevation Grid

The Elevation Grid section allows the user to select the elevation grid layer that is to be revised.

From the Select elevation grid layer dropdown combo box, select the source elevation grid. The dropdown combo box will list all the elevation layers that are currently used in the project.
Select elevation Grid Layer Dropdown Combo Box

Define Areas to Adjust Elevations

This section allows the user to define the portions of the existing elevation grid where the elevation value needs to be adjusted. The user can directly draw a polygon on the Map View or select existing closed polylines or polygons from the Map View to define the areas where elevation values will be adjusted.

When ready to draw a polygon on the Map View, click the [Draw] button. Use the Create curvilinear polygon checkbox option to make a smooth curvilinear boundary for the drawn polygon.
Adjust Elevations Dialog Box - Draw Button

The Adjust Elevations dialog box will temporarily disappear, and a prompt will be displayed on the status bar informing the user what to do next. Draw a polygon on the Map View, and then right-click and choose Done from the displayed context menu. The Adjust Elevations dialog box will be redisplayed.

Alternatively, click the [Pick] button and then select polygons or closed polylines from the Map View. Then, right-click and select Done from the displayed context menu. The Adjust Elevations dialog box will be redisplayed.

Apply Elevation Change to Polygon Areas

This section controls the elevation adjustment to be applied to the drawn or selected polygon areas. Three options are provided for adjusting the elevation, including:

  • Set elevation: This option defines a specific elevation for the selected region.
  • Add elevation offset: This option raises or lowers the elevation of the selected region by the specified value.
  • Multiply with scale factor: This option modifies the elevation by multiplying it by the defined scaling factor.

Apply Elevation Change to Polygon Areas Section

Terrain Slope Intersect

The Cut slope (V:H) and Fill slope (V:H) checkbox fields allow the user to match the elevation of the newly formed terrain with an existing terrain surface so that the newly formed terrain does not start or end gradually. By default, the Cut slope (V:H) and Fill slope (V:H) ratios are set to 1:1, which corresponds to a 1 ft (m) rise/down to a 1 ft (m) run. A ratio of 1:0 represents a vertical wall. However, many times a flatter slope is required, such as 1:2 or 1:3 for a smoother transition between terrains.
Terrain Slope Intersect Section

If the Cut slope (V:H) or Fill slope (V:H) checkbox entries are left unchecked, then the software will create a vertical face to intersect with the existing terrain and will not compute a daylight line to intersect with the ground terrain.

Revised Elevation Grid

This section is used to define the specifications of the revised elevation grid.

Click the […] browse button for the Elevation grid file entry to specify the file name and directory location to save the revised elevation grid file.

By default, the Load elevation grid as map layer checkbox option is checked to load the revised elevation grid as a layer in the Map Data Layers panel. Click the pencil icon to rename the layer.

The user can select the CRS to be used for the revised elevation grid. By default, the software uses the project CRS.

The Overwrite existing elevation layer checkbox option is checked by default to automatically overwrite an existing elevation layer (if one exists) with the revised elevation grid layer.

After the elevation grid options have been defined, click the [Adjust] button and the software will generate the revised elevation grid file and optionally load the DEM file as a layer in the Map Data Layers panel.
Revised Elevation Grid Section

About the Author Chris Maeder

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